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An inexact science

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Doctors consider some guidelines when mulling the antibiotic question, although it's still a gray area. It’s difficult to distinguish a severe viral infection from a mild-to-moderate bacterial infection based on symptoms alone.

So physicians often use their spider senses—a combination of experience and science—when deciding to dole out an antibiotic.

Here are five things most doctors take into consideration when making that decision.

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Fever

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If you have fever, shakes, and chills, you could have a bacterial infection, but those are also common with a viral illness such as the flu. Physicians will weigh your likelihood of having the flu—Is it circulating in your area at the moment? How many patients has he or she seen with the flu that day?—against the possibility of a bacterial infection.

If you have a fever and flu is circulating in your community, you'll probably leave the doctor's office without an antibiotic. Next year, get a flu shot.

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How long you've been sick

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Viral infections that hang around for a while can sometimes morph into a bigger problem, such as a sinus infection, and bacteria may join the party. So if your symptoms have been lingering for weeks, your likelihood of getting an antibiotic goes up.

However, most of the time, long-standing symptoms are due to a virus, not bacteria, so it’s still not the best way to determine your need for antibiotics.

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Testing

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A lab test is the only ironclad way to determine if you truly need an antibiotic.

A physician can collect a sample of bodily gunk (whatever you can cough up or blow out of your nose) or take a throat swab. In general, a culture, in which bacteria are grown in the lab and tested, can take a day or two. Doctors often forgo the expense and time of a lab test if they think they can make a best-guess decision based on the above symptoms.